Investigations are performed to explore high-repetition-rate femtosecond laser ablation effects on the physical and chemical properties of poly(methyl methacrylate) (PMMA). A scanning electron microscopy (SEM) is used to characterize the morphology change in the laser-ablated regions. The infrared and Raman spectroscopy reveals that the fundamental structure of the PMMA is altered after laser ablation. We demonstrate the cumulative heating is much greater during high-repetition-rate femtosecond laser ablation, supporting a photothermal depolymerization mechanism during the ablation process.